Beads comprising polymeric material are commonly used as base matrix for chromatography media and the most commonly used polymeric material is agarose. Agarose is ideal as a base matrix because of its minimal non-specific absorption, hydrophilicity, strong chemical resistance to e.g. base and solvents, high porosity and abundance of OH-groups for cross-linking and functionalization. One class of chromatographic media comprises one or more core particle(s) with an agarose coating on the outside. Such beads are, in particular, useful for fluidized bed adsorption because the density of such beads must be controlled to counter the buoyancy of the fluidizing flow, but may also be used as ion-exchange and affinity packed-bed media.
A common method of making agarose beads is by contacting an aqueous liquid comprising agarose with a hydrophobic liquid in a stirring vessel. This batch process is often used for making both homogeneous and cored beads. The agarose solids are suspended in water in the presence of the core material and then heated to or above the melting point of the agarose (about 90° C.). The hot agarose solution is then poured into a hot hydrophobic fluid in a stirring vessel. The hydrophobic fluid can be a solvent such as toluene or mineral oil. Since the aqueous agarose solution and the hydrophobic fluid don't mix, constant agitation turns the two liquids into an emulsion with the core material surrounded by the hot agarose solution as small droplets suspended in the hydrophobic fluid. Normally, a surfactant soluble in the phobic fluid is added to stabilize the small droplets so they don't coalesce into larger ones. The emulsion is then gradually cooled in the stirring tank about 30-300 minutes to solidify the droplets into gelled beads. The beads may then be washed and sieved to narrow the distribution to the useful range.
In EP 1 764 151 (same as US 2007/0069408) a different method for producing agarose or agarose beads with a solid core is described. The process involves dissolving/melting the agarose in a suitable liquid, mixing it with a hydrophobic liquid to form an emulsion and maintaining that emulsion at a temperature equal to or greater than the gelation point of the agarose, passing the emulsion through a static mixer to create agarose droplets and solidifying the agarose droplets in a second bath of hydrophobic liquid. The beads can then be recovered by decanting or centrifugation separation. The beads may be washed and used or further processed to crosslink the agarose and/or add various functionalities on to the agarose. EP 1 764 151 uses a static mixer instead of a stirring vessel to minimize non-uniformities in the agarose bead formation and in order to create a continuous method for making the beads.
In CN 1457919 A is disclosed a method for preparing a high density core material coated with a thin shell medium of agarose gel by preparing a suspension and emulsifying in a salad oil under the addition of emulsifier. Beads are formed by cooling in the same reactor.
In the prior art most disclosures are directed to bench scale methods in which the whole method, heating, emulsifying and cooling, takes place within the same reaction vessel over a period of 30 minutes or more. In actual mass production scale, or industrial scale production, the process time, in particular the cooling time, may be much longer. A further problem in the prior art disclosures is that the methods described in the prior art are either not continuous methods or insufficient shear forces are being used when providing the emulsion of core particles; polymeric material (e.g. agarose) and hydrophobic liquid to provide high density beads preferably of a small average size avoiding or minimizing coalescing of beads into larger aggregated beads and irregular lumps.
Thus, instead of bulky batch methods, it is desirable to use a truly continuous process for bead production, such as high density bead production. Although various types of bead production methods are researched and documented, patents and literatures are silent when it comes to a continuous industrial scale production of beads, such as high density beads.
Hence, it is desirable to provide an improved method and an improved system for producing beads, such as high density beads, and in particular a continuous industrial scale production of beads, such as high density beads being of highly regular spherical shape and of small average particle size with minimal bead aggregation. The present invention provides such a process.